Typical rubber hoses, for example, made of a blend of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend) which is excellent in resistance to gasoline permeability, have been used for conveying fuel (fuel such as gasoline for engine) for automobiles or the like in view of their high vibration-absorbability, easy assembling or the like. However, for the purpose of global environment protection, the regulations have been recently tighten against permeation of fuel for automobiles or the like, and are anticipated to be further tighten in the future. Therefore, such hoses for conveying fuel are required further permeation resistance to fuel.
And, hoses for conveying fuel such as hydrogen gas used in fuel cells, or for conveying carbon dioxide gas refrigerant are required extremely high permeation resistance to such conveyed fluid as hydrogen gas, carbon dioxide gas.
However, with regard to this requirement hoses configured by organic materials only such as rubber or resin are difficult to satisfy such required resistance.
Under the circumstances, it is considered to form preferably a composite hose by combining with a corrugated metal tube as a barrier layer against permeation of conveyed fluid.
For example, U.S. Pat. No. 6,354,332 discloses a composite hose with a corrugated metal tube of this type.
Meanwhile, a corrugated shape or a performance based on the shape provides a corrugated metal tube with an effect of flexibility. A material of the corrugated metal tube itself is metal and does not have elasticity different from rubber or the like.
So, a hose combined with a such corrugated metal tube involves a problem that during conveying fluid, an internal pressure is repeatedly exerted to the corrugated metal tube, the corrugated metal tube is deformed repeatedly in a radially expanding and contracting manner, and then a stress, which acts on the corrugated metal tube, brings a result that the corrugated metal tube is readily fatigue-broken at an early stage.
Specifically, when the corrugated metal tube expands radially, a maximum or large pulling stress or the largest pulling stress acts on corrugation hills. And, when it is repeated, the corrugation hills are readily cracked in a circumferential direction.
On the other hand, corrugation valleys are distorted and deformed while the corrugated metal tube expands and contracts radially. And, due to repeated distortion and deformation, the corrugation valleys are also readily cracked in a circumferential direction.
In the composite hose with a corrugated metal tube of this type which have been proposed traditionally, an elastic material such as rubber fills in valley gaps between corrugation hills on an outer peripheral side of the corrugated metal tube. The elastic material penetrating in the valley gaps as a result serve to restrain above deformation of the corrugation hills and the corrugation valleys of the corrugated metal tube.
However, in case of a conventional composite hose with a corrugated metal tube, the above-mentioned elastic material penetrating in the valley gaps are provided without an intention of restraining excessive deformation of the corrugation hills and valleys of a corrugated portion.
Then, the inventors of the present invention manufactured a sample of a composite hose with a corrugated metal tube where an elastic filler layer is provided to fill in valley gaps between corrugation hills on an outer peripheral side of the corrugated metal tube with an intention of restraining excessive deformation of the corrugated metal tube, specifically, of corrugation hills and valleys thereof, and evaluate the sample.
FIG. 7(.) shows one example thereof as comparison example.
With reference to FIG. 7(A), reference numeral 200 indicates a composite hose with a corrugated metal tube (hereinafter just referred to as a hose), which includes a corrugated metal tube 202 as an innermost layer by way of a barrier layer against permeation of conveyed fluid. A radial outer side of the corrugated metal tube 202 is laminated in sequence with a rubber filler layer 204, a first reinforcing layer 206, a middle rubber layer 208, a second reinforcing layer 210 and an outer surface rubber layer (cover rubber layer) 212.
Here, the first reinforcing layer 206 carries a function for pressure resistance when an internal pressure is exerted. The first reinforcing layer 206 is formed by braiding a reinforcing thread made of organic fiber, at a braid angle larger than a neutral angle (about 55°).
The first reinforcing layer 206 serves to restrain the hose 200 entirely from deforming in an expanding manner when an internal pressure is exerted.
The expansion restraint effect acts also on the corrugated metal tube 202. The first reinforcing layer 206 also serves to restrain the corrugated metal tube 202 from deforming in an expanding manner when an internal pressure exerted.
With reference to FIG. 7(B), reference numeral 214 indicates a corrugation hill of the corrugated metal tube 202, specifically of a corrugated portion thereof, reference numeral 216 indicates a corrugation valley thereof, and reference numeral 218 indicates a valley gap defined between adjacent corrugation hills 214, 214 on an outer peripheral side of the corrugated metal tube 202.
The above rubber filler layer 204 penetrates in the valley gaps 218, thereby serves to restrain deformation of the corrugated metal tube 202 in an expanding manner and excessive deformation of the corrugation hills 214 and the corrugation valleys 216.
So, as shown in FIG. 7(B), if no filler is filled in the valley gap 218 between the corrugation hills 214, 214 of the corrugated metal tube 202, and the valley gap 218 is vacant, the corrugated metal tube 202 is readily deformed and expands entirely in a diametrically expanding direction, when an internal pressure is exerted.
During that time, an excessive pulling stress acts on the corrugation hills 214, while the corrugation valleys 216 are largely distorted and deformed.
On the contrary, as shown in FIG. 7(C), if the valley gap 218 is filled with the rubber filler layer 204, such deformation is restrained. Owing to this restraint effect, it is prevented that the corrugation hills 214 are subject to the excessive pulling stress or the corrugation valleys 216 are excessively distorted and deformed. And, consequently, this prevents that the corrugated metal tube 202 is deformed excessively in an expanding manner and an excessive stress is generated in the corrugation hills 214 and the corrugation valleys 216. Hence, it was expected to cause no crack in the corrugated metal tube 202 at an early stage even when an internal pressure is exerted repeatedly to the corrugated metal tube 202 and consequently to improve durability of the corrugated metal tube 202.
However, a durability test (impulse test or impulse durability test) was conducted where an internal pressure is exerted to the hose 200 repeatedly at intervals, and it was found that the hose 200 does not necessarily have sufficient durability.
The cause of its insufficient durable life was pursued and turned out to be as follows. In the hose 200 as shown in FIG. 7(A), the rubber filler layer 204 is provided on an outer peripheral side of the corrugated metal tube 202 so as to have a certain radial thickness measured radially outwardly from a radial position of tops of the corrugation hills along an entire axial length of the corrugated metal tube 202 or a corrugated portion. So, expansion restraint effect of the first reinforcing layer 206 does not work on the corrugated metal tube 202 sufficiently and effectively. The corrugated metal tube 202 is deformed radially outwardly in an expanding manner, while the rubber filler layer 204 is elastically deformed. Then, due to this reason, the corrugated metal tube 202 comes to the end of its durable life and cracks at a relatively early stage when an internal pressure is exerted thereto repeatedly.
Contrary to the above as shown in FIG. 7(D), in case where whole amount of rubber content of the rubber filler layer 204 is small and this rubber filler layer 204 does not penetrate in the valley gaps 218 sufficiently, the corrugated metal tube 202 also does not have favorable durability.
The reason is that as space is left unfilled within the valley gaps 218 to receive rubber, the rubber is readily allowed to escape into unfilled space within the valley gaps 218, and the rubber filler layer 204 does not perform a sufficient function of restraining the corrugated metal tube 202 from being deformed.
The present invention is made under the foregoing circumstances. It is an object of the present invention to solve a problem that a corrugated metal tube is deformed excessively in radially expanding and contracting manner under an internal pressure exerted repeatedly, resulting in a fatigue crack initiation in the corrugated metal tube at an early stage, and to provide a composite hose with a corrugated metal tube having a favorable durable performance.